SAQ Grimeton – Alexanderson day June 2019

By   30 June 2019 21:22

This weekend, the VLF station in Grimeton was having an Alexanderson day. On Sunday June 30th, two transmissions were announced.

Although I read about the station several times and watched various YouTube videos, I never tried reception myself. On Saturday, I tested a number of wire antennas that were connected to a USB sound interface, running Spectrum Lab for reception, hoping that it would work. Some VLF stations could be heard and I knew that it was receiving. But was it good enough for SAQ?

About half past 10 local time, the live video showed the operators switching on the transmitter. After a few minutes of hearing just noise, I checked the Twenthe web SDR and confirmed that SAQ was indeed transmitting. A bit disappointing, but I suspected that local man made noise could blanket the signal, which it did.

Afternoon transmission
Luckily, a second chance was coming later that day. In the past, I tried a loop/coil antenna for VLF and about 100 metres of wire was wound around a little frame that was to be put into an aluminium case. The case shields electric fields and that helped to improve reception, I remembered.

The coil was put into the case and a BNC feedtrough part was used to connect a coax cable to the “antenna case”. The laptop was put on a garden table and the antenna was placed next to the pool.

20190630_SAQ_RX_PA2S

It was working! Although reception was somewhat less good than the Twenthe SDR, readability was good and the message could be copied without a problem.

Here is a recording, started just before 12.00 UTC.

There is definitely room for improvement. Man made noise is a huge problem and using a computer as SDR is not a very good choice. The spectogram shows the noise around the receive frequency.

20190630_SAQ_RX_PA2S_Screen

It is envisaged to build a VLF upconverter and use an analogue receiver. A better antenna is to be constructed as well.

A sincere thanks to all at SAQ for keeping the station in such a good condition and for offering the possibility to go back in time.